android: add Java-side support for browser compositor async readback

ui/base/android/window_android.h

Index: ui/base/android/window_android.h
diff --git a/ui/base/android/window_android.h b/ui/base/android/window_android.h
index 7e3918488f021d71161801375f911235a3ff19e2..df8685d0f0d084aacfd679252259c3c5fcf64482 100644
--- a/ui/base/android/window_android.h
+++ b/ui/base/android/window_android.h
@@ -36,9 +36,6 @@ class UI_BASE_EXPORT WindowAndroid {
     content_offset_ = content_offset;
   }
 
-  bool GrabSnapshot(int content_x, int content_y, int width, int height,
-                    std::vector<unsigned char>* png_representation);
-
   // Compositor callback relay.
   void OnCompositingDidCommit();